Thermal overload protective device

ABSTRACT

A thermal overload protective circuit breaker for removing power from a load, such as ballast device, when the load becomes overheated. The thermal overload protective circuit breaker uses an actuator, including a thermally expansible material, to separate the contacts, which are spring biased in a closed circuit position. The spring anneals on severe overloads causing the thermal overload protective circuit breaker to fail safe.

United States Patent 11 1 Alley et al. 1 1 July 3, 1973 [54] T ERM ()VE D TE IVE 2,915,899 12/1959 Vernet et a] 73/3682 DEVICE 2,724,030 ll/l955 Hilgert 337/320 X 2,789,184 4/1957 Matthews... 337/320 X [75] Inventors: Robert P. Alley; Mason H. Earing, 2,022,907 12/1935 Worley 337/320 both of Danville, lll. 2,798,130 7/1957 Cox 73/368 X [73] Assignee: General Electric Company, Fort Wayne, lnd. Primary Examiner-Bernard A. Gilheany Assistant Examiner-D. A. Tone [22] Flled 1972 Attorney-John M. Stoudt, Radford M. Reams et a1. [21] Appl. No.: 222,952

[57] ABSTRACT 52 US. Cl ..337114 337121, 337 315, 1 l 3370326 A thermal overload protective c1rcu1t breaker for re- 51 1 1m. c1. l-lOlh 87/00 Wing Power fmm a such as balm device when [58] Field of Search 337/114 115 118 bemmes The thermal Overload 337/121 122 327 326 329 protective circuit breaker uses an actuator, including a 6 thermally expansible material, to separate the contacts, which are spring biased in a closed circuit position. The 56] References Cited spring anneals on severe overloads causing the thermal UNITED STATES PATENTS overload protective circuit breaker to fail safe.

2,717,123 9/1955 Hilgcrt et a1 337/320 X 8 Claims, 2 Drawing Figures 16 14 L9 i i 1e 1 THERMAL OVERLOAD PROTECTIVE DEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a protective apparatus and, more particularly, to an apparatus for opening the current path for a lamp ballast or other device that may become overheated due to the current flowing through it. Ballast devices become overheated and destroy themselves when an excessive current flows through them due to a fault condition in the load circuit. Therefore, it is very desirable to detect the condition of a ballast beginning to overheat and to open the current path in which the ballast is located before the ballast device destroys itself.

2. Description of the Prior Art It is known in the art that certain materials such as paraffine, resin, and pitch, which are solid at ordinary room temperatures will liquify and expand at higher temperatures. The use of these heat expansible materials to operate a spring loaded switch is also known in the art. However the prior art devices use a piston-type arrangement in which the piston is driven by the expanding material and is mechanically coupled to the electrical contacts in order to separate the electrical contacts. These prior art devices have the disadvantage of requiring some kind of expansible container for the actuating expansible material, in both its solid and liquid phases, and generally involve sealing problems necessitating precise control of the manufacture of these devices to avoid leakage, which can render these devices inoperative.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an improved thermal overload protective apparatus.

It is another object of this invention to provide a thermal overload protective apparatus in which the electrical contacts are separated directly by the expansion of a material, having substantial thermal expansion associated with a change in phase of the material, dispersed in a resilient carrier.

Another object of this invention is to provide a thermal overload protective device in which the electrical contacts automatically close after minor faults, but which fail safe or remain in an open condition upon the occurrence of a major fault.

Another object of this invention is to provide a thermal overload protective apparatus which uses a thermally expansible material which exhibits a rapid increase in volume at approximately 110 centigrade.

A further object of this invention is to provide a thermal overload protective apparatus which uses a thermally expansible material to actuate the apparatus, but which does not require a separate expansible container for the thermally expansible material.

A still further object of this invention is to provide a thermal overload protective apparatus which can be compactly packaged preferably in a cylindrical shape.

Briefly stated, in accordance with one aspect of the invention, an insulating cylindrical element or holder is provided with a stationary contact element and a movable contact element, each of which is mounted on a shaped contact carrying element. The movable shaped contact carrying element is spring biased to normally keep the contacts in a closed position. Both contact carrying elements and the spring are conductive and leads are attached to the stationary contact carrying element and to the end of the spring opposite the shaped movable contact carrying element. An actuator, in- 5 cluding the thermally expansible material, is located within the cylindrical element between the contact carrying elements, and causes the movable contact to separate from the stationary contact when the apparatus exceeds a predetermined temperature. The actuator may be a dispersion of a thermally expansible material, such as dimethylsulfone, for example, dispersed in a resilient material, for instance a cured urethane elastomer. This eliminates any need for an expansible container to hold the expansible material. The spring is selected so that it will be annealed upon the occurrence of an excessive electrical current overload thereby causing the apparatus to fail open.

BRIEF DESCRIPTION OF THE DRAWING While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, the invention itself, as well as further objects and advantages thereof, may be better understood from the following description taken in connection with the accompanying drawing in which:

FIG. 1 is a cross-sectional view taken across a diameter and along a longitudinal axis of a thermal overload protective apparatus incorporating one embodiment of the invention; and

FIG. 2 is a cross-sectional view taken across a diameter and along a longitudinal axis of a thermal overload protective apparatus incorporating another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing and particularly FIG. 1, there is shown a thermal overload protective apparatus having a tubular housing 11 which may be formed from any suitable insulating material which is fairly rigid. A stationary contact carrying member or element 12 is firmly mounted in the housing as by force fitting, crimping, or cementing into position in the housing 11. Stationary contact carrying element 12 is provided with a lead 13 and a contact element 14 integrally formed thereon. The contact carrying element 12, contact element 14 and lead 13 form a stationary contact 15. The contact 15 may be formed from a single piece of conductive material or may be formed by mechanically and electrically joining a number of individual pieces.

A generally cylindrical actuator 16 is mounted cir-' cumferentially about the contact element 14 inside of the insulating housing 11. The actuator 16, of the illustrative exemplification, is formed as a dispersion composed of a thermally expansible material such as dimethylsulfone dispersed in a resilient carrier such as a cured urethane elastomer, which will be discussed in more detail hereinafter.

A shaped, movable contact carrying member or element 17, carrying movable contact element 18, is slidably received in the insulating housing 11 so that the contact elements 14 and 18 are in cooperative relationship. The movable shaped contact carrying element 17 may be cone shaped as shown in FIG. 1, or any other appropriate shape which provides sufficient space for the actuator 16. The movable shaped contact carrying element 17 is spring biased to a normally closed contact position by a conductive, resilient means such as spring 19. The end of spring 19 which is opposite that of the movable contact carrying element 17 engages a terminal plate 20 having a lead 21 formed integrally therewith. Contact carrying element 17 and contact element 18 form a movable contact 22. The contact may be form ed from a single piece of electrically conductive material or from two pieces of material which are electrically and mechanically joined together.

Referring now to FIG. 2, there is shown a cross sectional view taken across the diameter and along a longitudinal axis of a thermal overload proective apparatus 24 incorporating another embodiment of the invention wherein a tubular insulating housing 25 has slots 26a and 26b formed therein. Stationary contact carrying element 27 with contact element 28 integrally formed therein is thereon into the suitable shaped slot 26a and may be cemented therein to provide a stationary contact 29. An extension of the stationary contact carrying element 27 is formed to provide a terminal 30. A shaped, movable contact carrying element 31, having a movable contact element 32 formed integrally therewith is mounted in the housing 25 so that the contact elements 28 and 32 are in cooperative relationship. The contact carrying element 31 is formed with two cylindrical sections 33, 34 joined by a generally radially extending section 35. Thelarger diameter cylindrical section 33 is slidably received in the housing 25 while the contact element 32 is formed on the distal end of the smaller diameter section 34. Thus the contact carrying element 31 and contact element 32 form a movable contact 36. Movable contact 36 is biased to a position with contact elements 28,32 in engagement by a conductive spring 37. Spring 37 is mounted between the generally radial section 35 and a terminal plate 38. The terminal plate 38 is mounted in a suitably shaped slot 26b in housing 25 and may be restrained in place by any suitable means, such as by being cemented in place. The terminal plate 38 extends out of the housing 25 and is formed with terminal 39.

A generally cylindrical or tubular actuator 40 is provided in the space around cylindrical section 34 and extends generally between stationary contact carrying element 27 and the radially extending section 35 of movable contact carrying element 36. The actuator preferrably is formed from a dispersion composed of a thermally expansible material, such as dimethylsulfone, dispersed in a resilient carrier, such as a cured urethane elastomer.

The actuator 16 or 40 is preferably dimethylsulfone dispersed in a cured urethane elastomer which can be molded to the proper shape either externally or in situ. Dimethylsulfone dispersed in a cured urethane elastomer is preferred as the cured urethane elastomer is an elastic material which does not liquify, thus the actuator does not require the use of an expansible container and yet is capable of greatly increasing its volume because of the increase in volume of the dimethylsulfone, which is held in the cured urethane elastomer in the form of a dispersion. Dimethylsulfone has important properties in that it melts at approximately I l centigrade and is reasonably inert and therefore, does not react with or dissolve in the urethane elastomer. Also, while the dimethylsulfone may expand slightly as its temperature rises while it is a solid, such change in volume is small as compared to the change in volume associated with its change in phase between solid and liquid states. Thus the volumetric change in the actuator occurs substantially at the temperature at which the dimethylsulfone changes phase. A ballast device should be removed from the line when its temperature reaches approximately 1 10 centrigrade, and thus the use of dimethylsulfone as filler in the elastomer is ideal because dimethylsulfone melts at this temperature with a large expansion in its volume, thereby causing a large expansion in volume of the elastomer, which results in the opening of contacts 15, 22 or 29, 36. Also, a heat conductive filler material may be added to the elastomer system to increase its heat transfer capabilities thereby ensuring more effective operation.

A suitable dispersion of dimethylsulfone dispersed in a cured urethane elastomer was prepared from the mixture of the following chemical compounds measured by weight:

Chemical Compound Percent by Weight Urethane polyol 30% The urethane elastomer system was composed of urethane polyol and urethane prepolymer based on polyoxypropylene polyols and prepolymers prepared from such polyols by reaction with toluene diisocyanate. This polyol and a hydroxyl number of 56.0, a functionality of 2.7 to 3.0 hydroxyls per molecule, and a molecular weight of approximately 3,000. The polyol was prepared by the base-catalyzed addition of propylene oxide to glycerine. It had a viscosity of 445 cps at 25C and an unsaturation value of less than 0.04 meg/g. Products of this type are obtainable from BASF Wyandotte under the trade name PLURACOL GP3030. The prepolymer was prepared from this polyol by reaction with an /20 mixture of tolylene diisocyanate isomers. Sufficient tolylene diisocyanate was used to allow substantially all of the hydroxyl groups of the polyol to react with one of the two isocyanate groups of the toluene diisoyanate. The emulsifying agent consisted of equal parts of stearic acid, a block-polymer prepared by the reaction of propylene oxide and ethylene oxide with ethylene diamine of molecular weight 5500, and viscosity of 850 cps at 25 (obtained from BASF Wyandotte as TETRONlC 704 and a c amine oxyethylated with 1.0 mole of ethylene oxide (obtained from Rohm and Haas, Corporation as PRIMOX R-IM). Other emulsifying agents and combinations may be employed providing that they promote the dispersion of the meltable filler, dimethylsulfone, and do not interfere with the subsequent urethane reaction. The prepolymer, polyol the emulsifying agent, and the dimethylsulfone were heated to 120 centigrade and rapidly stirred to produce a dispersion of the insoluble molten dimethylsulfone in the urethane intermediates. The dispersion was then placed in a proper form at l20l25 centigrade for forty-five minutes to cure the urethane elastomer. The time for curing may be reduced by the addition of catalysts such as dibutyl tin dilaurate, stannous octoate and suitable amines, as is well known in the art. On cooling below centigrade, the dispersed dimethylsulphone solidified. Although this is a preferred method of producing the heat expansible material 14, the meltable filler also may be incorporated into the polymers by various methods such as miling and grinding.

In view of the fact that the operation of the exemplification thermal overload protective apparatus FIGS. 1 and 2 is substantially identical, only the operation of that illustrated in FIG. 1 will be described in detail. In operation, the thermal overload protective apparatus may be mounted in thermal contact with the ballast device and the leads or terminals of the thermal overload protective device connected in series with the ballast circuit. Upon simple overheating of the ballast device, the actuator 16 expands against the bias force of spring 19 forcing movable contact carrying element 17 with its contact element 18 away from stationary contact carrying element 12 with its stationary contact element 14. Upon separation of the contacts elements 14, 18 the ballast circuit is opened and the ballast device begins to cool. Upon sufficient cooling, the actuator 16 contracts, thereby allowing movable contact carrying element 17 to be moved towards the stationary contact carrying element 12 under the force of spring 19. The greatest portion of the movement of the actuator and thus the opening and closing of the contacts 15, 22 is associated with the phase change of the thermally expansible material in the actuator. Thus the thermal overload protective device can protect the ballast device during moderate intermittent overtemperatures and continue to operate effectively, by reclosing each time the temperature falls. However, should a large current overload occur, the current flowing through the ballast device and the thermal overload protection device will cause the spring 19 to anneal and thereby lose its spring compression force, and the heat generated in the ballast device will cause the actuator 16 to expand and open the contacts 15, 22 by moving contact carrying element 17 away from the stationary contact carrying element 12. Upon subsequent cooling of the ballast device, the overload protective device will not reclose because of the lack of spring force in spring 19 which is needed in order to move movable contact carrying element 17 toward the stationary contact carrying element 12.

It will be apparent to those skilled in the art that various changes and modifications may be made in the structure of the thermal overload protective circuit breakers described, or that different materials may be used to produce the same result in the circuit breakers above described. For example, fillers other than dimethylsulfone may be employed in various other elastomeric materials. The main criteria for the dispersed fillers are that they melt at the desired operating temperature of the device with a substantial increase in volume and that they not react with or dissolve substantially in the elastomer. Also it is preferable that the filler chosen be stable for extended periods of time. Examples of other fillers which may be used are iodoform (melting point 1 19C), acetanilid (melting point ll4C) and l, 3, S-Tribromobenzene (melting point 120C). Also, the tiller may be a low temperature melt ing metal alloy of the type set forth in copending application Ser. No. 783,764, filed Dec. 13, 1968, entitled Ternary Fusable Alloy, in the name of Rolf A. Ibscher, and assigned to the assignee of the present invention. The metal alloy described in the copending application of Rolf A. Ibscher has a melting point temperature in the range of 1 to 1 14 centigrade. However, ifa low temperature melting alloy is used as a filler material, the surface of the elastomer should be coated with a dielectric film to prevent conduction and shorting of the contacts when open. Also, if the dispersion is created by milling or grinding, as mentioned above, rather than by the emulsion polymerization of the urethane, other elastomers such as natural rubber, butyl rubber, nitrile rubber or flexible thermoplastic epoxy resin may be used as the elastomeric material in which the filler is dispersed.

in view of the above, it will be apparent that modifications and variations are possible within the scope and spirit of the above teachings. It therefore is to be understood that within the scope of the appended claims, the invention may be practiced other than as specifically described.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A thermal overload protective apparatus, comprising:

a. an enclosure;

a first electrical contact in said enclosure;

a second electrical contact in said enclosure; means biasing said first and second contacts into engagement; and

e. an actuator including a thermally volumetrically expansible material, having a substantial change in volume associated with a change in phase thereof dispersed in an elastomeric material, said actuator being operatively mounted between said first and second contacts to separate said first and second contacts upon the occurrence of an increase in the temperature sensed by said apparatus to a level sufficient to cause a phase change of said thermally expansible material.

2. A thermal overload protective apparatus as claimed in claim 1 and wherein said actuator is composed of dimethylsulfone dispersed in a cured urethane elastomer.

3. A thermally responsive circuit interrupting apparatus as claimed in claim 1 wherein said means biasing said first and second contacts into engagement is an electrically conductive spring connected in circuit with said first and second contacts, said conductive spring becoming annealed at a predetermined current overload to allow the thermally responsive circuit interrupting to permanently open.

4. A thermal overload proective apparatus, comprising:

a. an enclosure;

b. a stationary contact mounted in said enclosure, a

first lead connected to said stationary contact;

c. a movable contact movably mounted in said enclosure and engagable with said stationary contact, said movable contact and said stationary contact being formed to provide a space therebetween;

d. a conductive resilient means mounted in conductive engagement with said movable contact and biasing said movable contact into engagement with said stationary contact;

e. a second lead attached to said conductive resilient means at a point spaced from the portion of said resilient means on conductive contact with said movable contact; and

f. an actuator composed of a thermally volumetrically expansible material, having a substantial change in volume associated with a change in phase thereof, dispersed in an elastomeric material,

said actuator being located in the space between said stationary contact and said movable contact for disengaging said contacts upon said actuator reaching the temperature associated with the change in phase of said thermally volumetrically expansible material.

5. A thermal overload protective apparatus as claimed in claim 4 wherein said thermally volumetrically expansible material is composed of dimethylsulfone.

6. A thermal overload protective apparatus claimed forth in claim 4 wherein said elastomeric material is a cured urethane elastomer.

7. A thermally responsive circuit interrupting apparatus as claimed in claim 4 wherein said conductive resilient means is a spring which will become anneal at a predetermined current overload to allow the thermally responsive circuit interruptint to permanently open.

8. A thermal overload protective apparatus, comprising:

a. an enclosure;

b. a stationary electrical contact mounted in said enclosure, a first lead connected to said stationary contact;

c. a movable electrical contact movably mounted in said enclosure and engagable with said stationary contact, said movable contact and said stationary contact being formed to provide a space therebetween;

(1. an electrically conductive spring mounted in conductive contact with said movable contact and biasing said movable contact into engagement with said stationary contact;

. a second lead attached to said conductive spring at a point spaced from the portion of said conductive spring in conductive engagement with said movable contact;

. an acuator composed of a thermally volumetrically expansible material, having a substantial change in volume associated with a change in phase thereof, dispersed in an elastomeric material, said actuator being located in the space between said stationary contact and said movable contact for repeatedly disengaging said contact upon said actuator temperature rising above the phase change temperature of said actuator and for allowing said contacts to be closed by said spring upon the temperature of said actuator falling below the phase change temperature of said actuator; and

said conductive spring becoming annealed upon a predetermined current flow through said spring to allow said actuator to permanently open said contacts. 

1. A thermal overload protective apparatus, comprising: a. an enclosure; b. a first electrical contact in said enclosure; c. a second electrical contact in said enclosure; d. means biasing said first and second contacts into engagement; and e. an actuator including a thermally volumetrically expansible material, having a substantial change in volume associated with a change in phase thereof dispersed in an elastomeric material, said actuator being operatively mounted between said first and second contacts to separate said first and second contacts upon the occurrence of an increase in the temperature sensed by said apparatus to a level sufficient to cause a phase change of said thermally expansible material.
 2. A thermal overload protective apparatus as claimed in claim 1 and wherein said actuator is composed of dimethylsulfone dispersed in a cured urethane elastomer.
 3. A thermally responsive circuit interrupting apparatus as claimed in claim 1 wherein said means biasing said first and second contacts into engagement is an electrically conductive spring connected in circuit with said first and second contacts, said conductive spring becoming annealed at a predetermined current overload to allow the thermally responsive circuit interrupting to permanently open.
 4. A thermal overload proective apparatus, comprising: a. an enclosure; b. a stationary contact mounted in said enclosure, a first lead connected to said stationary contact; c. a movable contact movably mounted in said enclosure and engagable with said stationary contact, said movable contact and said stationary contact being formed to provide a space therebetween; d. a conductive resilient means mounted in conductive engagement with said movable contact and biasing said movable contact into engagement with said stationary contact; e. a second lead attached to said conductive resilient means at a point spaced from the portion of said resilient means in conductive contact with said movable contact; and f. an actuator composed of a thermally volumetrically expansible material, having a substantial change in volume associated with a change in phase thereof, dispersed in an elastomeric material, said actuator being located in the space between said stationary contact and said movable contact for disengaging said contacts upon said actuator reaching the temperature associated with the change in phase of said thermally volumetrically expansible material.
 5. A thermal overload protective apparatus as claimed in claim 4 wherein said thermally volumetrically expansible material is composed of dimethylsulfone.
 6. A thermal overload protective apparatus claimed forth in claim 4 wherein said elastomeric material is a cured urethane elastomer.
 7. A thermally responsive circuit interrupting apparatus as claimed in claim 4 wherein said conductive resilient means is a spring which will become anneal at a predetermined current overload to allow the thermally responsive circuit interruptint to permanently open.
 8. A thermal overload protective apparatus, comprising: a. an enclosure; b. a stationary electrical contact mounted in said enclosure, a first lead connected to said stationary contact; c. a movable electrical contact movably mounted in said enclosure and engagable with said stationary contact, said movable contact and said stationary contact being formed to provide a space therebetween; d. an electrically conductive spring mounted in conductive contact with said movable contact and biasing said movable contact into engagement with said stationary contact; e. a second lead attached to said conductive spring at a point spaced from the portion of said conductive spring in conductive engagement with said movable contact; f. an acuator composed of a thermally volumetrically expansible material, having a substantial change in volume associated with a change in phase thereof, dispersed in an elastomeric material, said actuator being located in the space between said stationary contact and said movable contact for repeatedly disengaging said contact upon said actuator temperature rising above the phase change temperature of said actuator and for allowing said contacts to be closed by said spring upon the temperature of said actuator falling below the phase change temperature of said actuator; and g. said conductive spring becoming annealed upon a predetermined current flow through said spring to allow said actuator to permanently open said contacts. 